1. Technical Field
The present invention relates to an antiglare film having little haze and excellent antiglare properties, as well as an image display with such an antiglare film.
2. Background of the Invention
Visibility of image displays, such as liquid crystal displays, plasma displays, Braun tube (cathode ray tube: CRT) displays and organic electroluminescence (EL) displays is significantly deteriorated when external light is reflected from the display surface. In order to reduce such reflection of external light, a layer for reducing reflection of external light is laminated on the surface of conventional image displays, such as those of television sets and personal computers, of which the image quality is important, video cameras and digital cameras used outdoors, where external light is strong, and cellular phones, which display using reflected light. The layer can be generally categorized into two kinds, such as one on which an anti-reflection is carried out using the interference in optical multilayer films, and the other on which an anti-glare process for scattering incident light so that reflected images fade is carried out by creating microscopic unevenness on the surface. From among these, it is necessary to form a multilayer film having a uniform optical film thickness in the former anti-reflection film, and therefore, the cost increases. In contrast, the latter antiglare films can be manufactured at relatively low cost, and therefore, are widely used in applications such as large personal computers and monitors.
Antiglare films as those described above have been manufactured in accordance with a conventional method for creating random unevenness on a sheet by applying a resin solution in which a filler is dispersed to a base sheet so that the filler is exposed from the surface of the applied film through adjustment of the thickness of the applied film. However, the arrangement and form of the unevenness on antiglare films manufactured by dispersing such a filler are influenced by the state of distribution of the filler in the resin solution or the state of application, and therefore, unevenness as intended may not sufficiently performed, and sufficient antiglare performance may not be gained. Furthermore, in the case where such a conventional antiglare film is placed on the surface of an image display, the entirety of the display surface becomes whitish due to scattering of light, causing that the surface becomes of a cloudy color, that is to say, so-called discoloring to white easily occurs. In addition, in the case where an antiglare uneven surface is provided on the outermost surface of an image display with high precision, pixels and unevenness on the antiglare surface sometimes interfere, causing so-called “glaring,” and the clarity of the image may be lowered. Such “glaring” lowers the visibility of the displayed image.
Meanwhile, it has been attempted to provide antiglare properties with only microscopic unevenness created on the surface of the transparent resin layer, without a filler. For example, JP2002-189106A (Claims 1 to 6, paragraphs 0043 to 0046) (Patent Document 1) discloses an antiglare film in such a form that an ionizing radiation curing resin layer is provided on a transparent resin film by curing the ionizing radiation curing resin in a state where the ionizing radiation curing resin is sandwiched between the emboss mold and the transparent resin film, so that microscopic unevenness is created, where the average coarseness at ten points in three dimensions and the average distance between adjacent protrusions on the three-dimensional coarseness reference surface respectively have predetermined values.
In addition, JP H6 (1994)-34961A (Claims 1 to 3, paragraph 0024) (Patent Document 2), JP2004-45471A (Claim 4, Embodiment 1) (Patent Document 3) and JP2004-45472A (Claim 4, Embodiment 1) (Patent Document 4), for example, disclose use of a film where microscopic unevenness is created on the surface as a light diffusing layer placed on the back side of a liquid crystal display instead of an antiglare film placed on the display surface of a display.
As a technique for creating unevenness on the surface of a film, the above described Patent Documents 3 and 4 disclose a method where an emboss roll having such a form that protrusions and recesses are inverted is filled with an ionizing radiation curing resin liquid, a transparent base which runs in sync in the direction of rotation of an engraving roll makes contact with the filling resin, the resin between the engraving roll and the transparent base is cured when the transparent base makes contact with the engraving roll, the cured resin and the transparent base are attached to each other at the time of curing, and after that, the layered body of the resin after curing and the transparent base is peeled from the engraving roll.
In this technique, the composition of the ionizing radiation curing resin solution that can be used is restricted, and leveling, such as through application of a liquid distilled with a solvent, may be expected to be insufficient, and therefore, the uniformity of the film thickness may not be sufficient. Furthermore, it is necessary to fill the engraving emboss roll directly with a resin liquid, and therefore, high physical precision is required in the engraving emboss roll in order to secure uniformity on the uneven surface, and thus, it is difficult to fabricate an emboss roll.
Next, the above described Patent Document 2, for example, discloses a method for preparing a cylindrical body using a metal or the like and creating unevenness on the surface of the cylindrical body in accordance with a technique such as electronic sculpting, etching or sandblasting as a method for fabricating a roll used for the fabrication of a film having unevenness on the surface. In addition, JP2004-90187A (Claims 1 and 2) (Patent Document 5) discloses a method for fabricating an emboss roll including steps of forming a metal plating layer on the surface of an emboss roll, polishing the surface of the metal plating layer to a mirror surface, carrying out a blasting process using ceramic beads on the surface of the metal plating layer that has been polished to a mirror surface, and carrying out a peening process if necessary.
In the state where a blasting process has been carried out on the surface of the emboss roll as described above, distribution in the diameter of unevenness corresponds to the distribution in the particle diameter of the blasting particles, and it is difficult to control the depth of recesses gained through blasting, and thus, it may be difficult to gain unevenness in a form which is excellent in antiglare performance with high reproducibility.
In addition, the above-described Patent Document 1 describes the creation of a surface with unevenness in accordance with a sandblasting method or a bead shooting method, preferably using a roller where chromium is plated on the surface of iron. Furthermore, it is described that it is preferable for the mold where unevenness is created on the surface in this manner to be used after chromium is plated on the surface for the purpose of increasing durability at the time of use, and thereby, hardening of the film and prevention of corrosion can be achieved. Meanwhile, the above described Patent Documents 3 and 4 respectively describe Embodiment where the surface of iron is plated with chrome, a liquid sandblasting process of #250 is carried out, and after that, a chrome plating process is again carried out, and thereby, microscopic unevenness is created on the surface.
In this method for fabricating an emboss roll, blasting or shooting is carried out on the chromium plating having a high hardness, and therefore, it is difficult for unevenness to be created, as well as for the form of the created unevenness to be controlled with precision. Furthermore, the surface of the chromium plating generally tends to be coarse, and fine unevenness is created through chromium plating on the unevenness created through blasting, and therefore, it is difficult to design the manner in which unevenness is created. Moreover, the scattering properties in the finally gained antiglare film change in a negative manner due to the fine unevenness created through chromium plating.
Furthermore, JP2005-140890A (Claim 1, paragraph 0056) (Patent Document 6) by the present inventors discloses an antiglare film where the peak position and the half value width thereof satisfy predetermined conditions when regions which are higher than the average height of the unevenness are protrusions and regions which are lower than these are recesses, the frequency of apparent areas found from the projected area of an individual protrusion or recess is shown in a histogram. In this Patent Document, contrast in the front of a liquid crystal display formed by combining an antiglare film with a liquid crystal panel lowers when the haze is high, and therefore, it is preferable for the haze to be not more than 15%.